Sundial

ABSTRACT

An improved sundial comprising a reflective surface member supported in a plane parallel with the earth&#39;&#39;s axis and adapted to receive and reflect sun rays; a non-reflective line inscribed along said reflective surface parallel to the axis of the earth&#39;&#39;s rotation and adapted to project a shadow; a translucent semicylindrical member projected over said surface and co-axial about said line, the surface of said cylinder carrying a time scale observable from the exterior of the translucent member such that the shadow is highlighted by a bright sunlit outline of reflected sun rays with said shadow indicating the time of day.

United States Patent [191 Davies Jan. 22, 1974 SUNDIAL [76] Inventor: Robert H. Davies, 3831 Carson Cir.,

[52] US. Cl. 33/270 [51] Int. Cl. G04b 49/00 [58] Field of Search 33/269, 270, 271

[56] References Cited UNITED STATES PATENTS 2,524,706 10/1950 Johanson et al. 33/271 Primary Examiner-Robert B. Hull Attorney, Agent, or Firm--Thomas E. Schatzel et a].

An improved sundial comprising a reflective surface member supported in a plane parallel with the earths axis and adapted to receive and reflect sun rays; a non-reflective line inscribed along said reflective surface parallel to the axis of the earth's rotation and adapted to project a shadow; a translucent semicylindrical member projected over said surface and coaxial about said line, the surface of said cylinder carrying a time scale observable from the exterior of the translucent member such that the shadow is highlighted by a bright sunlit outline of reflected sun rays with said shadow indicating the time of day.

10 Claims, 3 Drawing Figures SUNDIAL BACKGROUND OF THE INVENTION The present invention relates to sundials. Sundials have been used since early man as a method of indicating solar time. Throughout their history, several varieties of sundials have been used. In the most part the prior art dials are crude in structure and commonly cumbersome to handle. Modern day sundials are commonly of complex structure and relatively expensive to manufacture.

SUMMARY OF THE PRESENT INVENTION The present invention relates to an improved sundial structure adapted to perform the function of an equatorial sundial, i.e., a sundial with a rod-shaped gnomon parallel to the axis of rotation of the earth with the shadow of the gnomon being projected on a scale. The present structure, however, utilizes a smooth, mirrorfinished, reflecting surface with a thin non-reflective line inscribed thereon. The reflecting surface is adapted to function as a mirror to reflect sun rays and project a shadow of the non-reflective line on a semicylindrical member. The shadow is highlighted on the semi-cylindrical member by a bright sunlit outline. The cylinder is scaled and claibrated in increments to designate the solar time.

The present invention provides for a highly accurate sundial of simplified structure and which is portable. The sundial may be adapted for ready universal use at any latitude or longitude on the earth. The sundial may include adjustment means for adjusting its horizontal angle to readily correspond to the earth s latitude at the location of use. The structure may further carry adjustment means for adjusting for the longitude of its location and for the equation of time at any given time during the year. When such adjustments are made, the sundial indicates mean time directly without the necessity for making corrections to the time indicated.

BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a perspective view of a sundial according to the present invention;

FIG. 2 is a perspective view of an alternative embodiment of the present invention; and

FIG. 3 is an enlarged bottom view of a section of the semicylindrical scalar member.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is depicted a perspective view of a sundial of the present invention and referred to by the general reference character 1. The sundial includes a support base 3 for supporting the structure on a horizontal plane. Projecting from the support base 3 is an angled column 5 having a first end 7 engaged horizontally with the base 3 and a second end 9 angled relative to the base 3 and supporting a reflecting surface support member 11. The support member 11 has a top planar surface 12 supported at an angle A relative to the horizontal plane of the support base 3. The angle A is selected to coincide with the degree of latitude of the earth at the location where the sundial 1 is used. Angle A may vary from zero, when the sundial is located at the equator to 90 when the sundial is located at a pole. A reflecting member 13, with a mirrorfinished, reflecting planar surface 15 is supported by the member 11 such that the planar surface 15 is supported at the angle A. The reflecting member 13 supports a non-reflecting line 17 inscribed thereon and extending end-to-end of the member 13 and surface 15 such that the line 17 is parallel to the earths axis. The reflecting surface 15 is adapted to be in line with rays from the sun and reflect said rays at an angle B corresponding to the angle of alignment of the sun rays relative to the reflective planar surface 15. The angle B continuously varies with the relative position of the earth and sun.

Laterally perpendicular to the member 13 and surface 15 is a lateral support member 19 comprising a pair of arms 19A and 19B projecting laterally from each side of the member 1 l. The arms 19A and 19B are each at a right angle to the line 17 and in a common plane parallel with the planar surface 15. Spanning across the support member 19 is a translucent semicylindrical member 21. The member 21 may be comprised of a translucent pliable, plastic material forming a half circle with the terminal ends terminating in a plane which plane is common to each of the terminating ends and the surface 15. The member 21 terminates at one end within a slot 23 of the arm 19A and at the other end within a slot 25 of the arm 198. The slots 23 and 25 are positioned at a radial distance R from the line 17. The distance R coincides with the radius of the are 21 such that the member 21 is of uniform radius throughout its path.

The translucent member 21 is sealed in increments to designate hours and partial hours of time. The illustrated cylinder 21 is sealed in twelve major increments, with each increment representing an hour of time. The hour increments are designated with a major time mark. Intermediate each major time mark hour marking is a plurality of eleven minor time marks, equally spaced relative to one another, to designate five-minute time intervals. The angular spacing between adjacent major time marks is fifteen angular degrees and the angular spacing between adjacent minor marks represents 1.25 angular degrees. The scale markings are numerically arranged in the clockwise direction such that the scale is read in the modern day manner. For example, the time marking adjacent to the slot 23 represents 6:00 A.M. and the time marking adjacent the slot 25 represents 6:00 P.M. High noon marking of 12:00 is positioned in vertical alignment with the non-reflective line 17.

In operation, the angle A is selected to coincide with the earths latitude at the location where the sundial is being used. The latitude at any given location on the earth s surface may be acquired by referring to a World Atlas. The sundial 1 is then positioned such that the inscribed line 17 is in alignment with the earths axis. This is realized by directing the line 17 to be in alignment with the earth's axis of rotation. When in alignment, rays from the sun are cast on the reflecting surface 15 and reflected on to the translucent member 21. The reflected rays project a shadow of the non-reflecting line 17 on to the translucent cylinder 21. The shadow on the member 21 is highlighted by a sunlit outline of the reflected sun rays. The position of the shadow may be read directly from the scale as representing solar time. For example, FIG. 1 illustrates a time of 4:00 P.M. At said time, sun rays are directed from a westwardly direction at the acute angle B relative to the reflecting surface 15. Uniform reflections of the light rays project from the surface 15 at the acute angle B toward the translucent member 21. The shadow of the line 17 is projected on the member 21 at the angle B such that the outline of the shadow is projected on the member 21 at the position indicating 4:00 P.M.

FIG. 2 depicts in perspective a universal sundial according to the present invention and referred to by the general reference character 51. The sundial 51 is adapted to correct for adjustments in the equation of time and for the longitude at the location of the sundial. Various of the elements of the sundial 51 are similar to those of the sundial 1 of FIG. 1. Accordingly, for purposes of clarity, those elements of the sundial 51 similar to the sundial I carry the same reference numeral distinguished by a prime designation.

The sundial 51 is adapted to provide a single sundial structure for universal use throughout the world. The base 3' includes angular position setting means for selectively setting the non-reflecting line 17' to be parallel with the earths axis at any latitude on the earths surface. The angular position setting means includes a groove 53 within the base 3'. Supported and positioned within the groove 53 is an arcuate support column 55. The support column 55 carries an arcuate edge which is co-axial with a line 56 perpendicular to the line 17' and the terminal edges of the member 21 The column 55 may be pivoted and adjustably positioned within the groove 53 to adjust the alignment of the line 17 to true north and parallel with the axis of rotation of the earth at any latitudinal position on the earths surface. The column 55 carries a concave top surface 57 supporting the reflecting surface support member 13 such that the angle A may be varied depending on the angular position of the column 55 within the groove 53 to equal the degree of latitude. The angle A may be varied from for use at the equator to 90 for use at a pole. The column 55 may be locked in place by means of an adjustment lock bolt 58. The bolt 58 is externally threaded about the terminal end and is supported within a channel 59 extending laterally within the base member 3. The channel 59 further supports a sleeve 61 which is internally threaded such that the threads of the bolt 58 and sleeve 61 intermesh. The tip of the bolt 58 is adapted to project through the sleeve 61 to within the groove 53. When projecting through the sleeve 61, the tip of the bolt 58 engages the sidewall of the column 55 to lock the column in a set position. Interlock of the bolt 58 and the column 55 may be made or released by turning the bolt 58 within the sleeve 61. The column 55 carries a latitude scale marked in angular increments such that an angle A may be selected to coincide with the latitude at the location where the sundial is to be used.

The base member 3' further carries an inscribed equation of time illustrated by a graphical representation 62. Sundials generally read solar time. A day in solar time, i.e., the time lapse from the time the sun is successively directly overhead may vary from twentyfour hours by plus or minus a few seconds depending on where the earth is in its ellipsoidal orbit about the sun. Over a years period, solar time may deviate from mean time by several minutes since the earths orbit about the sun is ellipsoidal. The equation of time inscribed on the base 3 sets forth the amount of time differential between solar time and mean time for any given day of the calendar year. The abscissa of the graph represents the calendar day of the year in solar time and the ordinate represents time in minutes. To acquire mean time from the indicated solar time, the correction for the equation of time is read from the equation of time graph and added to or subtracted from the designated solar time.

The depicted sundial 51 further includes means for adjusting for time deviations resulting from the equation of time and for the longitude at the location of use. The longitude location varies eastwardly about the equator from 0 at the prime meridian to at the international dateline and westwardly from 0 at the prime meridian to 180 at the international dateline. The boundaries of mean time zones are designated at approximately every 15 of longitude with there being a one hour time differential in mean time between adjacent time zones. Accordingly, for locations intermediate designated time zones, mean time and solar time deviates due to the longitudinal position intermediate designated time zones. For example, at the mid-point within a time zone, solar time and mean time may vary by as much as approximately thirty minutes relative to that at the easternly or westemly border of the time zone. Also, in some areas of the world, e.g., the United States, during certain time periods of the year mean time is recorded as daylight savings time, thereby deviating by one hour from standard time.

The sundial 51 includes angular adjustment means for adjusting the relative angular position of the member 21 to the planar surface 13'. The sundial 51' includes a reflecting surface member 13' as part of an arcuate member 65 positioned within the concave groove 57. The member 65 has an axis of rotation co-axial with the line 17'. The member 65 is adapted to be pivoted within the groove 57 about the non-reflective line 17' to adjust the angular position of the planar surface 13' relative to the sun and any given point on the member 21. To adjust the angular position, a worm gear assembly, referred to by the general reference character 67 is included. The gear assembly 67 includes a drive gear 69 with gear teeth inter-engaged with gear teeth 71 integral with the member 65. The shaft of the drive gear 69 projects to the side surface of the column 55 such that action of the gear assembly 67 may be controlled by a drive force imparted by a tool, e.g., a screwdriver. The member 65 carries an angular scale 72 about its front edge to designate the angular position of the planar surface 13 relative to a reference marker 73 carried about the front face of the column 55. Accordingly, depending on the location along the earth's longitudinal surface, and the deviation due to the equation of time, the member 65 may be adjustably pivoted about the line 17 either clockwise or counterclockwise responsive to a drive force applied to the drive gear 69. in making said adjustment, the relative position of any given point on the member 21' and the planar surface 13' is adjusted. In effect, when making the adjustment, the scale on the member 21' is advanced or retracted relative to reflections from the planar surface 13 depending on the nature of the adjustment. When properly adjusted the scale 21 reads mean time directly and takes into account deviations due to longitudinal location and equation of time. The member 57 further carries a ridge 75, slideably engaged within a groove 77 to secure the member within the groove 57.

To further aid in proper adjustment of the sundial 51 to correct for equation of time deviations, the equation of time may be graphically plotted on the underside of the semi-cylindrical member 21' with the high noon scalar increment common to the ordinate, as illustrated by FIG. 3. A graphical representation 81 of the equation of time is plotted on the underneath side of the cylinder. The graph 81 carries designations, J,F,M,A,M,J,J,A,S,O,N and D to represent each month of the calendar year. Accordingly, to correct for the equation of time for any given calendar day, the sundial 51 is viewed from directly above. The inscribed equation of time graphical representation 81 is reflected on the surface 13'. The gear assembly 67 is adjusted such that the given calendar day on the graph 81 is in direct alignment with the non-reflective line 17'. This in turn adjusts the angle B to compensate for the equation of time. The gear assembly may be further adjusted to compensate for the longitude position. The longitude adjustment may require adjustment for up to approximately 59 minutes 59 seconds depending on whether the dial 51' is located near the eastern boundary of the time zone or the western boundary. Further, to adjust between daylight savings time and standard time, the gear assembly 67 need be adjusted to compensate for the hour differential.

I claim:

1. A sundial comprising, in combination:

a support member for supporting a mirror-finished planar reflecting surface along an angle equal to the angle of latitude of the earth;

a reflecting member having a mirror-finished planar reflecting surface, the reflecting member being supported by the support member with said surface in a first plane parallel to said angle and including a non-reflective line inscribed on said surface along a path in alignment with the earths axis of rotation; and

a semi-cylindrical member co-axial with said nonreflective line, the semi-cylindrical member being supported by said support member and spanning over the reflecting member to receive sun-ray reflections from the reflecting member.

2. The sundial of claim 1 in which the semi-cylindrical member is inscribed with a scale having a plurality of spaced increments to represent time.

3. The sundial of claim 2 in which the semi-cylindrical member is comprised of a strip of pliable translucent material.

4. The sundial of claim 1 in which the semi-cylindrical member is comprised of a translucent member in which the shadow from said nonreflective line is highlighted by the reflected sunrays; and further including first angular-setting means for adjustably setting the angular position of said mirror-finished planar reflecting surface relative to the axis of rotation of the earth. Y

5. The sundial of claim 4 in which the support member is in the form of a vertical column member with an arcuate edge; and

the first angular-setting means includes a horizontal member carrying a groove with said arcuate edge of the support member positioned within said groove, said vertical column being pivotable about an axis extending through and normal to said nonreflective line.

6. The sundial of claim 5 in which the first angular-setting means further includes locking means for locking said vertical column in position relative to said horizontal member at a desired angle.

7. The apparatus of claim 2 further including angular adjustment means for adjusting the relative angular position of said planar surface to a given time on said scale of the semi-cylindrical member to said planar surface, said second angular adjustment means providing for relative angular advancement and retractment of reflections from said planar surface relative to said given time on said scale.

8. The apparatus of claim 1 in which the semi-cylindrical member is inscribed with a scale having a plurality of spaced increments to represent time;

first angular-setting means for adjustably setting the angular position of said mirror-finished reflecting planar surface relative to the axis of rotation of the earth; and

second angular adjustment means for adjusting the relative angular position of said planar surface to a given time on said scale of the semi-cylindrical member, said second angular adjustment means providing for advancement and retractment of reflections from said planar surface relative to said given time on said scale.

9. The apparatus of claim 8 in which the second angular setting means includes an arcuate member supporting said reflecting member, said arcuate member having an axis of rotation co-axial with said non-reflective line, a gear assembly engaged to the arcuate member for rotating the arcuate member about its axis of rotation, said gear assembly including a drive gear integral with said reflecting member and a drive gear for driving said driven gear, said drive gear including means for receiving a drive force to activate said gear assembly.

10. The apparatus of claim 9 in which the semi-cylindrica1 member is comprised of a translucent member in which the shadow from said nonreflective line is highlighted by the reflected sunrays, said semi-cylindrical member being inscribed with a scale having a plurality of spaced increments to represent time; and further including a graphical representation of the equation of time inscribed on the underside of the semi-cylindrical member about a given scalar indication and in alignment with said mirror-reflecting surface such that the outline of said graphical representation is reflected on said surface about said non-reflective line. 

1. A sundial comprising, in combination: a support member for supporting a mirror-finished planar reflecting surface along an angle equal to the angle of latitude of the earth; a reflecting member having a mirror-finished planar reflecting surface, the reflecting member being supported by the support member with said surface in a first plane parallel to said angle and including a non-reflective line inscribed on said surface along a path in alignment with the earth''s axis of rotation; and a semi-cylindrical member co-axial with said non-reflective line, the semi-cylindrical member being supported by said support member and spanning over the reflecting member to receive sun-ray reflections from the reflecting member.
 2. The sundial of claim 1 in which the semi-cylindrical member is inscribed with a scale having a plurality of spaced increments to represent time.
 3. The sundial of claim 2 in which the semi-cylindrical member is comprised of a strip of pliable translucent material.
 4. The sundial of claim 1 in which the semi-cylindrical member is comprised of a translucent member in which the shadow from said non-reflective line is highlighted by the reflected sun-rays; and further including first angular-setting means for adjustably setting the angular position of said mirror-finished planar reflecting surface relative to the axis of rotation of the earth.
 5. The sundial of claim 4 in which the support member is in the form of a vertical column member with an arcuate edge; and the first angular-setting means includes a horizontal member carrying a groove with said arcuate edge of the support member positioned within said groove, said vertical column being pivotable about an axis extending through and normal to said non-reflective line.
 6. The sundial of claim 5 in which the first angular-setting means further includes locking means for locking said vertical column in position relative to said horizontal member at a desired angle.
 7. The apparatus of claim 2 further including angular adjustment means for adjusting the relative angular position of said planar surface to a given time on said scale of the semi-cylindrical member to said planar surface, said second angular adjustment means providing for relative angular advancement and retractment of reflections from said planar surface relative to said given time on said scale.
 8. The apparatus of claim 1 in which the semi-cylindrical member is inscribed with a scale having a plurality of spaced increments to represent time; first angular-setting means for adjustably setting the angular position of said mirror-finished reflecting planar surface relative to the axis of rotation of the earth; and second angular adjustment means for adjusting the relative angular position of said planar surface to a given time on said scale of the semi-cylindrical member, said second angular adjustment means providing for advancement and retractment of reflections from said planar surface relative to said given time on said scale.
 9. The apparatus of claim 8 in which the second angular setting means includes an arcuate member supporting said reflecting member, said arcuate member having an axis of rotation co-axial with said non-reflective line, a gear assembly engaged to the arcuate member for rotating the arcuate member about it''s axis of rotation, said gear assembly including a drive gear integral with said reflecting member and a drive gear for driving said driven gear, said drive gear including means for receiving a drivE force to activate said gear assembly.
 10. The apparatus of claim 9 in which the semi-cylindrical member is comprised of a translucent member in which the shadow from said non-reflective line is highlighted by the reflected sun-rays, said semi-cylindrical member being inscribed with a scale having a plurality of spaced increments to represent time; and further including a graphical representation of the equation of time inscribed on the underside of the semi-cylindrical member about a given scalar indication and in alignment with said mirror-reflecting surface such that the outline of said graphical representation is reflected on said surface about said non-reflective line. 